When laying a foundation of a tower construction such as a wind turbine, a reinforced concrete element is often cast and subsequently, the turbine tower is positioned on the concrete element and fixed thereto. A simple way of fixing the tower to the concrete element is to anchor substantially vertical anchor rods in the concrete element, and attach these to a flange being attached to the tower wall.
U.S. Pat. No. 5,586,417 discloses an example of such a tower construction. The foundation is formed within a ground pit and externally and internally back filled. The lower end of the foundation has a circumferential ring fully embedded therein. Sets of inner and outer circumferentially spaced bolts have lower ends anchored to the ring, upper ends projecting up outwardly of the top of the foundation, and mid-portions free of connection with the cementitious material of which the foundation is constructed. The base flange of a tubular tower is positioned downwardly upon the upper end of the foundation with the upper ends of the inner and outer sets of bolts projecting upwardly through holes provided in the base flange. Nuts are threaded downwardly upon the upper ends of the bolts and against the base flange. The nuts are highly torqued in order to place the bolts in heavy tension and to thus place substantially the entire length of the cylindrical foundation in heavy axial compression.
A high strength grout may be used directly under the base flange of the tower to support the weight of the tower. Such a grout may not be desirable for the entire foundation, e.g. due to material costs. Therefore the grout is moulded on a base of concrete with a relatively lower strength.
It is important to provide a solid interface between the high strength grout and the relatively lower strength concrete, but use of the two different types of material increases moulding costs and the time consumption associated therewith.